A car bomb struck the entrance of a Turkish police station Sunday in the southern city of Gaziantep, killing two police officers and wounding 22 other people in a day marred by violence and May Day protests.

Four civilians were among those wounded in the explosion, according to Gov. Ali Yerlikaya of Gaziantep province. The blast shattered the windows of nearby buildings.

The police station is close to offices for the governor and mayor. Gaziantep is also home to the offices of international aid organizations focused on the conflict in neighboring Syria.

There was no immediate claim of responsibility for the attack. A Turkish interior ministry official, who spoke on condition of anonymity in line with government practice, said investigations were ongoing.

Speaking in Ankara, the Turkish capital, Prime Minister Ahmet Davutoglu expressed his condolences and wished a speedy recovery to those wounded in Gaziantep's "heinous terrorist attack."

Turkey has suffered multiple bombings in recent months linked either to Kurdish militants or the Islamic State group.

In the eastern provinces of Mardin, three Turkish soldiers were killed and 14 wounded in an attack by Kurdish militants, the military reported. Another was killed in clashes with PKK militants in the border province of Sirnak.

Later on Sunday, a car bombing targeted a gendarme station in the southeastern town of Dicle, Diyarbakir Province, according to the interior ministry official.

He told The Associated Press "a few soldiers were injured" when the "bomb-laden vehicle exploded." A local official gave a higher toll, saying one soldier was killed and 26 others, including civilians, were wounded in the attack.

The authorities were blaming the Dicle bombing on the Kurdistan Workers' Party, or PKK, a group designated by Ankara and its allies as a terrorist organization.

Meanwhile, another Kurdish militant group, known as the Kurdistan Freedom Falcons, claimed responsibility for a suicide attack in Bursa, Turkey's fourth largest city, which wounded 13 people on Wednesday.

Turkey, which is facing both growing blowback from the conflict in Syria and renewed conflict with Kurdish militants, has seen a rise of deadly attacks across the country. In the past year, more than 200 people across the country have been killed in six major bombings.

Sunday's violence eclipsed International Labor Day celebrations. In Gaziantep, demonstrations were canceled for security reasons.

Police in Ankara carried out anti-terror operations the night before and detained four suspected IS members allegedly planning to attack May Day demonstrators.

In Istanbul, police imposed tight security measures and used water cannons and tear gas on demonstrators who sought to rally in non-designated areas.

The office of the governor of Istanbul said 24,500 security officers reported for duty on Sunday and that 207 people were detained. One man died after being run over by a water cannon vehicle.

Elsewhere, eight people were wounded after four rockets hit Kilis, another town near the Syrian border, the state-owned Anadolu Agency reported. Three Syrians were among the injured.

The news agency said the Turkish military retaliated by firing at IS targets across the border in Syria, killing nine militants. It wasn't possible to verify the agency's claim.

Kilis, where Syrian refugees outnumber locals, has been hammered by cross-border fire since mid-January. There have been a total of 18 fatalities in that period.

The wider province of Kilis borders areas in Syria that are contested by Kurdish factions, IS militants and rebels fighting to topple Syrian President Bashar al-Assad.